The present invention relates to an isoparaffin-olefin alkylation process carried out in a circulating slurry reactor containing a slurry comprising fluidizable solid acid zeolite catalyst of particles whose largest dimension ranges from 20-2000 microns and liquid reactants and products, wherein a portion of said slurry is recycled at very high rates to provide a very high isoparaffin to olefin molar ratio, while a second portion of the slurry is passed to a separating means to separate reactants and products from the catalyst, regenerating the catalyst, optionally recycling the separate reactants to the reactor, and collecting the alkylate product which is useful, inter alia, as an octane enhancer for gasoline.
As a result of the curtailment in the use of tetraethyl lead as an octane-improving additive for gasoline, not only has the production of unleaded gasoline increased but the octane number specification of all grades of gasoline have increased as well. Isoparaffin-olefin alkylation is a key route to the production of highly branched paraffin octane enhancers which are to be blended into gasolines.
Alkylation involves the addition of an alkyl group to an organic molecule. Thus, an isoparaffin can be reacted with an olefin to provide an isoparaffin of higher molecular weight. Industrially, alkylation often involves the reaction of C.sub.2 -C.sub.5 olefins with isobutane in the presence of an acidic catalyst. Alkylates are valuable blending components for the manufacture of premium gasolines due to their high octane ratings.
In the past, alkylation processes have included the use of hydrofluoric acid or sulfuric acid as catalysts under controlled temperature conditions. Low temperatures are utilized in the sulfuric acid process to minimize the undesirable side reaction of olefin polymerization and the acid strength is generally maintained at 88-94 percent by the continuous addition of fresh acid and the continuous withdrawal of spent acid. The hydrofluoric acid process is less temperature-sensitive and the acid is easily recovered and purified.
The typical types of alkylation currently used to produce high octane gasoline blending component, that is, the hydrofluoric acid and sulfuric acid alkylation processes, have inherent drawbacks including environmental concerns, acid consumption and disposal of corrosive materials. With the increasing demands for octane and the increasing environmental concerns, it has been desirable to develop an alkylation process based on a solid catalyst system. The catalyst of the present invention offers a refiner a more environmentally acceptable alkylation process than the currently used hydrofluoric and sulfuric acid alkylation processes.
Crystalline metallosilicates, or zeolites, have been widely investigated for use in the catalysis of isoparaffin alkylation. For example, U.S. Pat. No. 3,251,902 describes the use of a fixed bed of ion-exchanged crystalline aluminosilicate having a reduced number of available acid sites for the liquid phase alkylation of C.sub.4 -C.sub.20 branched-chain paraffins with C.sub.2 -C.sub.12 olefins in which the molar ratio of isoparaffin to olefin is generally greater than 3 to 1. The patent further discloses that the C.sub.4 -C.sub.20 branched-chain paraffin should be allowed to substantially saturate the crystalline aluminosilicate before the olefin is introduced to the alkylation reactor.
U.S. Pat. No. 3,450,644 discloses a method for regenerating a zeolite catalyst used in hydrocarbon conversion processes involving carbonium ion intermediates.
U.S. Pat. No. 3,549,557 describes the alkylation of isobutane with C.sub.2 -C.sub.3 olefins using certain crystalline aluminosilicate zeolite catalysts, e.g., rare earth-exchanged zeolite Y, in a fixed, moving or fluidized bed system, the olefin being preferably injected at various points in the reactor.
U.S. Pat. No. 3,644,565 discloses the alkylation of a paraffin with an olefin in the presence of a catalyst comprising a Group VIII noble metal present on a crystalline aluminosilicate zeolite, the catalyst having been pretreated with hydrogen to promote selectivity.
U.S. Pat. No. 3,647,916 describes an isoparaffin-olefin alkylation process featuring the use of an ion-exchanged crystalline aluminosilicate, isoparaffin/olefin mole ratios below 3:1 and regeneration of the catalyst.
U.S. Pat. No. 3,655,813 discloses a process for alkylating C.sub.4 -C.sub.5 isoparaffins with C.sub.3 -C.sub.9 olefins using a crystalline aluminosilicate zeolite catalyst wherein a halide adjuvant is employed in the alkylation reactor. The isoparaffin and olefin are introduced into the alkylation reactor at specified concentrations and catalyst is continuously regenerated outside the alkylation reactor.
U.S. Pat. No. 3,893,942 describes an isoparaffin alkylation process employing, as catalyst, a Group VIII metal-containing zeolite which is periodically hydrogenated with hydrogen in the gas phase to reactivate the catalyst when it has become partially deactivated.
U.S. Pat. No. 3,236,671 discloses the use, in alkylation, of crystalline aluminosilicate zeolites having silica to alumina mole ratios above 3 and also discloses the use of various metals exchanged and/or impregnated on such zeolites.
U.S. Pat. No. 3,706,814 discloses another zeolite-catalyzed isoparaffin-olefin alkylation process and further provides for the addition of C.sub.5 + paraffins such as Udex raffinate or C.sub.5 + olefins to the alkylation reactor feed and the use of specific reactant proportions, halide adjuvants, etc.
U.S. Pat. No. 3,624,173 discloses the use, in isoparaffin-olefin alkylation, of zeolite catalysts containing gadolinium.
U.S. Pat. No. 3,738,977 discloses alkylation of paraffins with ethylene employing a zeolite catalyst which possesses a Group VIII metal component, the catalyst having been pretreated with hydrogen.
U.S. Pat. No. 3,865,894 describes the alkylation of C.sub.4 -C.sub.6 isoparaffin with C.sub.3 -C.sub.9 monoolefin employing a substantially anhydrous acidic zeolite, for example acidic zeolite Y (zeolite HY), and a halide adjuvant.
U.S. Pat. No. 3,917,738 describes a process for alkylating an isoparaffin with an olefin using a solid, particulate catalyst capable of absorbing the olefin. The isoparaffin and the olefin are admixed to form a reactant stream in contact with catalyst particles at the upstream end of an adsorption zone after which the reactants are passed concurrently with the catalyst so that a controlled amount of olefin is adsorbed onto the catalyst before the combination of reactants and catalyst is introduced into an alkylation zone. This controlled olefin adsorption is said to prevent polymerization of the olefin during alkylation.
U.S. Pat. No. 4,377,721 describes an isoparaffin-olefin alkylation process utilizing, as catalyst, ZSM-20, preferably HZSM-20 or rare earth cation-exchanged ZSM-20.
U.S. Pat. No. 4,065,381 describes a process utilizing a draft tube for hydrogen stripping of HF from an extract containing metal pentafluoride and HF resulting from hydrocarbon conversions using Friedel-Crafts catalysts, e.g., alkylation.
U.S. Pat. No. 4,384,161 describes a process of alkylating isoparaffins with olefins to provide alkylate employing as catalyst a large pore zeolite capable of absorbing 2,2,4-trimethylpentane, e.g., ZSM-4, ZSM-20, ZSM-3, ZSM-18, zeolite Beta, faujasite, mordenite, zeolite Y and the rare earth metal-containing forms thereof, and a Lewis acid such as boron trifluoride, antimony pentafluoride or aluminum trichloride. The use of a large pore zeolite in combination with a Lewis acid in accordance with this patent is reported to greatly increase the activity and selectivity of the zeolite thereby effecting alkylation with high olefin space velocity and low isoparaffin/olefin ratio.
U.S. Pat. No. 5,095,167 describes a process and apparatus for alkylating isoparaffin with an olefin which decreases catalyst inventory required while improving alkylate quality by internally admixing unreacted isoparaffin and alkylate product with the reactant stream in the draft tube of a decantation reaction vessel.
U.S. Pat. No. 4,992,615 describes a process for alkylating isoparaffins with olefins to provide alkylate using MCM-22 catalyst.
U.S. Pat. No. 4,918,255 describes a process for alkylating isoparaffin with olefin to provide a product having a high proportion of highly branched paraffins using a composite catalyst comprising a Lewis acid with large pore zeolite in the presence of a controlled amount of water. Suitable large pore zeolites include ZSM-3, ZSM-4, ZSM-12, ZSM-18, ZSM-20, zeolite Beta, zeolite L, mordenite, faujasite and Zeolite Y.
All of the above disclosures are incorporated herein by reference.
Processes employing solid catalysts suffer from problems in that the catalysts tend to age rapidly and are unable to perform effectively at high olefin space velocities unless they are promoted with a Lewis acid such as boron trifluoride, BF.sub.3, antimony pentafluoride, SbF.sub.5, and aluminum chloride, AlCl.sub.3. However, such promoted catalysts involve the use of corrosive and hazardous materials. Accordingly, although methods capable of using unpromoted solid acid catalysts would be desirable, such unpromoted catalysts are known to have a low selectivity for alkylation versus olefin polymerization and require frequent regeneration.